New proton radioactivities165,166,167Irand171Au

Abstract

The new proton radioactivities ${}^{165,166,167}\mathrm{Ir}$ and ${}^{171}\mathrm{Au}$ have been observed. The Ir isotopes were produced via the ${}^{92}\mathrm{Mo}{(}^{78}\mathrm{Kr}{,pxn)}^{165,166,167}\mathrm{Ir}$ reactions at 357 and 384 MeV. ${}^{171}\mathrm{Au}$ was produced via the ${}^{96}\mathrm{Ru}{(}^{78}\mathrm{Kr}{,p2n)}^{171}\mathrm{Au}$ reaction at 389 MeV. The proton emitters were each identified by position, time, and energy correlations between the implantation of a residual nucleus into a double-sided silicon strip detector, the observation of a decay proton, and the subsequent observation of a decay alpha particle from the daughter nucleus (${}^{164,165,166}$Os and ${}^{170}\mathrm{Pt},$ respectively). Both ${}^{166}\mathrm{Ir}$ and ${}^{167}\mathrm{Ir}$ have proton-emitting ground and isomeric states, which also decay by alpha emission. The proton-decay rates have been reproduced by calculations using the WKB barrier penetration approximation and a low-seniority shell-model calculation of the spectroscopic factors. The alpha decays of the four nuclei are followed by chains of alpha decays, allowing the determination of single-particle orbital orderings. Mass information has also been obtained from the alpha-decay chains because a connection to a known mass can be obtained for one of the nuclei. Ground-state mass excesses are reported for ${}^{151}\mathrm{Tm},$ ${}^{154}\mathrm{Yb},$ ${}^{155}\mathrm{Lu},$ ${}^{158}\mathrm{Hf},$ ${}^{159}\mathrm{Ta},$ ${}^{162}\mathrm{W},$ ${}^{163}\mathrm{Re},$ ${}^{166}\mathrm{Os},$ ${}^{167}\mathrm{Ir},$ and ${}^{170}\mathrm{Pt}.$ The mass excess for ${}^{171m}\mathrm{Au}$ is also given. Proton separation energies are also deduced for the odd-$Z$ alpha daughter nuclei of the Ir proton emitters.